Generally, the 3rd Generation Partnership Project (3GPP) for regulating technical standardizations of the third generation mobile communications system has been researching for LTE/SAE (Long Term Evolution/System Architecture Evolution) since the end of 2004 for an enhanced and optimized performance, in correspondence to several forums and new technologies relating to the 4th generation mobile communications system. The SAE developed mainly by 3GPP SA WG2 relates to a network technology for determining an architecture of a network and supporting mobility between heterogeneous access networks together with LTE of 3GPP TSG RAN. The SAE, one of important standardization issues is to develop the 3GPP system into an IP-based system for supporting various radio access technologies. For an optimized packet-based system with minimized transfer delay by an enhanced data transfer capability, research has been executed.
FIG. 1 is a configuration view of an Idle mode Signaling Reduction (ISR) service. FIG. 1 illustrates a routing area, tracking areas, and an ISR area.
Hereinafter, the technical terms used in the present invention will be explained with reference to FIG. 1.                TA (tracking area) indicates an area to which E-UTRAN provides a service, and includes one or more E-UTRAN cells. RA (routing area) indicates an area to which GERAN or UTRAN provides a service, and includes one or more GERAN/UTRAN cells.        TAI (Tracking Area Identity) list indicates a list of TAIs that identify the tracking areas (e.g., TA1, TA2, TA3, TA4 and TA5 in FIG. 1) that a UE can enter without performing a tracking area updating procedure. The TAI list has been defined in 3GPP TS 24.301 v9.1.0, and thus detailed explanations thereof will be omitted.        MME (Mobility Management Entity) area indicates a part of a network served by an MME. The MME area consists of one or several Tracking Areas. All cells served by one eNodeB are included in one MME Area. The MME area has been defined in 3GPP TS 23.002 v9.2.0, and thus detailed explanations thereof will be omitted.        Cell “camping on” (Camped on a cell) indicates that a UE has completed a cell selection/reselection process and has chosen a cell. The cell camping on has been defined in 3GPP TS 36.304 v9.1.0, and thus detailed explanations thereof will be omitted.        ISR (Idle mode Signaling Reduction) indicates a service to enhance efficiency of network resources by reducing signaling for location registration (location update) when the UE moves between different access networks such as E-UTRAN and UTRAN/GERAN. Referring to FIG. 1, the ISR will be explained in more detail. When the UE camps on the E-UTRAN cell, the UE performs location registration on the MME. On the other hand, when the UE moves to the UTRAN/GERAN cell and camps on that cell, the UE performs location registration on the SGSN. Therefore, when the UE frequently moves between the E-UTRAN and the UTRAN/GERAN, network resources may be wasted due to frequent location registration procedures. In order to reduce the waste of network resources, an ISR method has been proposed. According to the ISR method, once the UE respectively performs location registration on the MME and the SGSN (two mobility management nodes) via the E-UTRAN and the UTRAN/GERAN, the UE in an idle mode does not perform an additional location registration when moving between two pre-registered Radio Access Technologies (RATs), or when reselecting a cell. If there is downlink (DL) data that should be sent to a corresponding UE in an ISR activated state and an idle mode, paging is simultaneously delivered to the E-UTRAN and the UTRAN/GERAN. This allows the network to successfully search for the UE and to deliver the DL data to the UE. The ISR has been defined in 3GPP TS 23.401 v9.3.0 and 3GPP TS 23.060 v9.3.0, and thus detailed explanations thereof will be omitted.        ICS (IMS Centralized Services) stably provides consistent services based on IMS to the UE regardless of an access network to which the UE has attached (i.e., when the UE has attached not only to IP-CAN but also to a CS domain). The ICS has been defined in 3GPP TS 23.292 v9.4.0, and thus detailed explanations thereof will be omitted.        IMS (IP Multimedia Subsystem) indicates a system for providing a multimedia service based on an IP.        AS (Application Server) indicates a server for providing various multimedia services.        SCC AS (Service Centralization and Continuity Application Server) indicates an application server for supporting continuity of a multimedia session. The SCC AS has been defined in 3GPP TS 23.292 v9.4.0 and 3GPP TS 23.237 v9.3.0, and thus detailed explanations thereof will be omitted.        CSFB (Circuit Switched FallBack) indicates technique for providing voice and other CS domain services by making the UE which is in an E-UTRAN accessed state fallback to a UTRAN/GERAN CS domain accessed state. The CSFB has been defined in 3GPP TS 23.272 v9.2.0, and thus detailed explanations thereof will be omitted.        Intra-SGSN mobility: The UE camping on the UTRAN or GERAN moves to a new        
UTRAN or GERAN which belongs to a Routing Area (RA) different from the routing area on which the UE previously performed location registration. Here, since the previously location-registered RA and the new RA are served by the same SGSN, the UE performs location registration on the same SGSN. Referring to FIG. 2, the intra-SGSN mobility will be explained. In FIG. 2, it is assumed that the UE has performed location registration on the SGSN in the RA1, and then has moved to the RA2. Once entering the new RA (RA2), the UE performs location registration on the SGSN. This is called as ‘intra-SGSN mobility’.                Intra-MME mobility: The UE camping on the E-UTRAN moves to a new E-UTRAN. A tracking area (TA) to which the new E-UTRAN cell belongs is served by the MME on which the UE previously performed location registration. However, the TA is not included in a TAI list received from the MME when the UE previously performed location registration on the MME. Accordingly, the UE performs location registration on the same MME. Referring to FIG. 3, the intra-MME mobility will be explained. The UE has performed location registration on the MME in the TA3, and then moves to the TA4. In this case, the TA4 is not included in a TAI list (TAI list 1) received from the MME. Accordingly, the UE performs location registration on the MME, which is called as ‘intra-MME mobility’.        
Hereinafter, the present invention will be explained in more detail with reference to the aforementioned technical terms.
FIG. 4 is a signal flowchart showing ISR activation in a network in accordance with the conventional art. Referring to FIG. 4, once the UE 10 initially camping on the E-UTRAN cell moves to the GERAN or UTRAN cell (S4-5), the UE 10 camps on the GERAN or UTRAN cell.
FIG. 4 illustrates procedures (S4-1˜S4-4) to attach to the MME 20 by the UE 10 currently camping on the E-UTRAN, a procedure (S4-5) to reselect the GERAN or UTRAN as the UE 10 moves, routing area update procedures (S4-6˜S4-13) with respect to the GERAN or UTRAN on which the UE camps on, and a procedure (S4-14) to reselect the E-UTRAN by the UE 10 as the UE 10 moves back to the E-UTRAN cell.
Hereinafter, an ISR activation process will be explained in more detail with reference to FIG. 4.
Once the UE 10 initially camps on the E-UTRAN cell, the UE 10 sends an Attach Request message to the MME 20 for location registration on the HSS 40 through the MME 20 via the eNodeB 21 (S4-1). The MME 20 sends an Update Location Request message to the HSS 40 so as to inform the UE's attachment (S4-2).
The HSS 40 stores an identity (ID) of the MME 20 to which the UE 10 has attached, and sends an Update Location Ack message including the UE's subscriber information to the MME 20 (S4-3). The MME 20 sends an Attach Accept message to the UE 10 via the eNodeB 21 (S4-4). Through S4-1˜S4-4, the UE 10 completes to attach to the MME 20 which serves the currently camped E-UTRAN cell, and registers the UE's location on the HSS 40.
Then, the UE 10 moves to a coverage area of the GERAN or UTRAN cell, thereby reselecting the GERAN or UTRAN cell (S4-5). This requires for the UE 10 to perform Routing Area Update on the GERAN or UTRAN cell for location registration (S4-6 S4-13).
More concretely, the UE 10 sends a Routing Area Update Request message to the SGSN 30 so as to perform location registration on the HSS 40 through the SGSN 30 via the RNC/BSC 31 (S4-6). Through the Routing Area Update Request message, the SGSN 30 can recognize that the UE 10 has performed location registration on the MME 20 in the previous steps (S4-1˜S4-4). The SGSN 30 sends a Context Request message to the MME 20 so as to receive context information on the UE 10 from the MME 20 on which location registration has been performed through S4-1˜S4-4 (S4-7).
As a response to the Context Request message sent from the SGSN 30, the MME 20 sends a Context Response message including context information on the UE 10 to the SGSN 30 (S4-8). Here, the MME 20 includes an ‘ISR Supported’ parameter in the Context Response message so as to inform the SGSN 30 that the MME 20 can support an ISR feature. The UE's context information included in the Context Response message includes MM (Mobility Management) Context information, and EPS PDN Connections information. Here, the EPS PDN Connections information includes Bearer Context information. The MME 20 constitutes context information on the UE 10 which is to be included in the Context Response message, based on the MM context information and EPS bearer context information. The MM context information and the EPS bearer context information maintained by the MME have been defined in clause 5.7.2 (MME) of 3GPP TS 23.401 v9.3.0, and thus detailed explanations thereof will be omitted.
The SGSN 30 decides whether it activates an ISR feature for the UE 10 (S4-9). More concretely, the SGSN 30 can recognize that the MME 20 supports an ISR feature by analyzing the ‘ISR Supported’ parameter included in the Context Response message received from the MME 20. Since the SGSN 30 also supports an ISR feature, the SGSN 30 decides to activate an ISR feature.
Since both of the MME 20 and the SGSN 30 support an ISR feature, in S4-9, the SGSN 30 decides for ISR activation. As a response to the Context Response message sent from the MME 20, the SGSN 30 sends a Context Ack message to the MME 20 (S4-10). Here, the SGSN 30 informs the MME 20 that an ISR feature for the UE 10 has been activated, by including an ‘ISR Activated’ parameter in the Context Ack message.
Once the ISR feature has been activated, the SGSN 30 and the MME 20 store each mutual identity (ID). And, the MME 20 having received the Context Ack message including the ‘ISR Activated’ parameter from the SGSN 30 continuously keeps (maintains) the context information on the UE 10.
The Context Request message of S4-7, the Context Response message of S4-8, and the Context Ack message of S4-10 have been defined in clause 7.3.5 (Context Request), 7.3.6 (Context Response) and 7.3.7 (Context Acknowledge) of 3GPP TS 29.274 v9.1.0, and thus detailed explanations thereof will be omitted.
The SGSN 30 sends an Update Location Request message to the HSS 40 so as to inform the UE's location registration (S4-11). And, the HSS 40 stores an identity (ID) of the SGSN 30 on which the UE 10 has performed Routing Area Update, and sends an Update Location Ack message including the UE's subscriber information to the SGSN 30 (S4-12).
The SGSN 30 sends a Routing Area Update Accept message to the UE 10 through the RNC/BSC 31 (S4-13). Here, the SGSN 30 informs the UE 10 ISR activation by including the ‘ISR Activated’ parameter in the Routing Area Update Accept message.
Through the attach procedures (S4-1˜S4-4) and the routing area update procedures (S4-6˜S4-13), the UE has performed location registration, and ISR activation has been performed since both of the MME 20 and the SGSN 30 support an ISR feature.
Thereafter, even if the E-UTRAN is reselected as the UE 10 moves to the E-UTRAN from the GERAN or UTRAN (S4-14), the UE 10 does not have to perform location registration on the MME 20 since an ISR feature has been activated.
More concretely, after the ISR activation, the UE 10 does not have to perform location registration again on the network unless it leaves the routing area registered through the SGSN 30, or the tracking area(s) registered through the MME 20. This feature (function) is ISR. A combined area of the routing area registered by the UE 10 through the SGSN 30, and the tracking area(s) registered by the UE 10 through the MME 20 is called as an ISR area (refer to FIG. 1). When the UE frequently moves between the E-UTRAN and the UTRAN/GERAN, waste of network resources may be reduced by omitting repetitive location registration procedures under the ISR feature.
FIG. 5 is a signal flowchart showing ISR activation in a network in accordance with the conventional art. More concretely, FIG. 5 shows that the UE 10 initially camping on the GERAN or UTRAN cell moves to the E-UTRAN cell (S5-5), and then camps on the E-UTRAN cell. A cell on which the UE 10 has initially camped in FIG. 5 is different from that in FIG. 4 (i.e., GERAN or UTRAN cell in FIG. 5 and E-UTRAN cell in FIG. 4). Accordingly, an operation and a function of each signaling in FIG. 5 correspond to those in FIG. 4. Therefore, explanations for each signaling in FIG. 4 can be applied to a corresponding signaling in FIG. 5. Signals transmitted through the eNodeB 21 in FIG. 4 are transmitted through the RNC/BSC 31 in FIG. 5, and vice versa.
Hereinafter, with reference to FIGS. 6 and 7, will be explained keeping an ISR activated state in case of intra-SGSN mobility and intra-MME mobility.
FIG. 6 is a signal flowchart showing that an ISR activated state is kept in case of intra-SGSN mobility in accordance with the conventional art.
FIG. 6 shows that an ISR activated state is kept in case of the UE's intra-SGSN mobility. As the UE moves to another GERAN or UTRAN cell from the GERAN or UTRAN cell, the UE performs location registration on the SGSN. Here, it is assumed that the previously location-registered SGSN and the newly location-registered SGSN are same (i.e., intra-SGSN mobility).
S6-1˜S6-13 of FIG. 6 are equal to S4-1˜S4-13 of FIG. 4, and thus detailed explanations thereof will be replaced by those of FIG. 4. Hereinafter, will be explained S6-14˜S6-17 of FIG. 6, i.e., a location registration process on the SGSN 30 by the UE 10 as the UE moves to the new GERAN or UTRAN cell (i.e., intra-SGSN mobility), and a process for deciding to keep ISR activation by the SGSN 30.
The UE 10 moves to a new GERAN or UTRAN cell. Then, the UE 10 recognizes that a Routing Area (RA) to which the new GERAN or UTRAN cell belongs is different from the previously location-registered RA, and decides to perform location registration (S6-14).
For location registration on the HSS 40 through the SGSN 30, the UE 10 sends a Routing Area Update Request message to the SGSN 30 through the RNC/BSC 31 (S6-15). Here, the UE 10 includes an old RAI (Routing Area Identity) parameter in the Routing Area Update Request message.
The SGSN 30 determines whether to keep or deactivate an activated ISR for the UE (S6-16). If a Routing Area Update (RAU) procedure performed by the UE 10 based on the decision by the SGSN 30 is an intra-SGSN RAU procedure, the currently activated ISR feature is kept. After checking the old RAI parameter included in the Routing Area Update Request message received from the UE 10, the SGSN 30 recognizes that the old RA is also served by itself (i.e., intra-SGSN RAU procedure). Accordingly, the SGSN decides to continuously keep (maintain) the currently activated ISR feature.
A Routing Area Update Accept message is transmitted from the SGSN 30 to the UE 10 through the RNC/BSC 31 (S6-17). Here, the SGSN 30 includes an ‘ISR Activated’ parameter in the Routing Area Update Accept message, thereby informing the UE 10 about decision for ISR activation. The Routing Area Update Accept message may include a Routing Area Identity (RAI).
In summary, in FIG. 6, when the UE performs intra-SGSN mobility after an ISR feature is activated, the SGSN 30 on which the UE performs location registration determines to keep the activated ISR feature.
FIG. 7 is a signal flowchart showing that ISR activation is kept in case of the UE's intra-MME mobility.
That is, FIG. 7 shows that an ISR activated state is kept in case of the UE's intra-MME mobility. Referring to FIG. 7, as the UE moves to another E-UTRAN cell from the E-UTRAN cell, the UE 10 performs location registration on the MME 20. Here, it is assumed that the previously location-registered MME 20 and the newly location-registered MME 20 are same (i.e., intra-MME mobility). It is also assumed that a Serving GW has no changes in case of the intra-MME mobility.
FIG. 6 shows that ISR activation is kept in case of intra-SGSN mobility, whereas FIG. 7 shows that ISR activation is kept in case of intra-MME mobility. Therefore, explanations for each signaling in FIG. 6 can be applied to a corresponding signaling in FIG. 7. Hereinafter, FIG. 7 will be explained in brief.
S7-1˜S7-14 of FIG. 7 are equal to S5-1˜S5-14 of FIG. 5, and thus detailed explanations thereof will be replaced by those of FIG. 5. Hereinafter, will be explained S7-15˜S7-19 of FIG. 7, i.e., a location registration process on the MME 20 by the UE 10 as the UE moves to the E-UTRAN cell (i.e., intra-MME mobility), and a process for deciding to keep ISR activation by the MME 20.
The UE 10 moves to a new E-UTRAN cell. Then, the UE 10 performs location registration in a Tracking Area (TA) to which the new E-UTRAN cell belongs (S7-15). The reason why the UE 10 has to perform location registration is because the TA to which the UE 10 has entered is not included in a TAI list received through a Tracking Area Update Accept message of S7-14 when the UE 10 previously performed location registration on the MME 20.
For location registration on the HSS 40 through the MME 20, the UE 10 sends a Tracking Area Update Request message to the eNodeB 21 (S7-16). Here, the UE 10 sends a Radio Resource Control (RRC) parameter including an old GUMMEI (Globally Unique MME Identifier), together.
Based on the RRC parameter received from the UE 10 together with the Tracking Area Update Request message, the eNodeB 21 determines an MME 20 to which the Tracking Area Update Request message is to be forwarded. Then, the eNodeB 21 forwards (transfers or delivers) the Tracking Area Update Request message to the determined MME 20 (S7-17). In FIG. 7, it is assumed that the MME 20 which serves the new TA to which the UE 10 has entered is the same as the MME 20 on which the UE 10 has previously performed location registration (S7-6˜S7-14).
The MME 20 determines to keep or deactivate an activated ISR feature for the UE 10 (S1-18). If the Serving GW has not changed, the MME 20 decides to keep an activated ISR feature since location registration has been performed on the same MME 20 as the previous MME 20.
The MME 20 sends a Tracking Area Update Accept message to the UE 10 through the eNodeB 21 (S7-19). Here, the MME 20 includes an ‘ISR Activated’ parameter in the Tracking Area Update Accept message, thereby informing the UE 10 about decision for ISR activation. The Tracking Area Update Accept message includes a TAI (Tracking Area Identity) list.
In FIG. 7, when the UE 10 performs intra-MME mobility after an ISR feature is activated, the MME 20 on which the UE performs location registration decides to keep the activated ISR feature unless the Serving GW is changed.
FIG. 8 is a signal flowchart showing data transfer on a downlink when an ISR feature has been activated. In FIG. 8, it is assumed that an ISR feature has been activated through the processes of FIG. 4 or FIG. 6. FIG. 8 shows a method for delivering downlink data to the UE which is in an idle mode when an ISR feature has been activated. For convenience, it is assumed that the UE of FIG. 8 is camping on the E-UTRAN cell.
A Serving GW (‘S-GW’) 50 receives a downlink data packet destined to the UE 10 through a P-GW 60 (S8-1). The S-GW 50 buffers the downlink data packet, and identifies a mobility management node serving the UE 10, a receiver of the downlink data packet. Through this identification procedure by the S-GW 50, it is checked that an ISR feature for the UE 10 has been activated, and both of the MME 20 and the SGSN 30 serve the UE 10. Accordingly, the S-GW 50 has to request both of the MME 20 and the SGSN 30 to perform paging for the UE.
More concretely, the S-GW 50 sends a Downlink Data Notification message to the MME 20 and the SGSN 30, respectively (S8-2). As a response to the Downlink Data Notification message, the MME 20 and the SGSN 30 send a Downlink Data Notification Ack message to the S-GW 50, respectively (S8-3).
The MME 20 and the SGSN 30 send a paging message to the UE 10 through each serving access network (S8-4a˜S8-5a and S8-4b˜S8-5b). This will be explained in more detail as follows.
The MME 20 sends a paging message to each eNodeB 21 included in the tracking area(s) on which the UE 10 has registered (S8-4a). The SGSN 30 sends a paging message to the RNC/BSC 31 (S8-4b).
Each eNodeB 21 having received the paging message from the MME 20 performs paging for the UE 10 (S8-5a). And, the RNC/BSC 31 having received the paging message from the SGSN 30 performs paging for the UE 10 (S8-5b).
In an assumption that UE 10 currently camps on the E-UTRAN cell, the UE 10 responds to the paging via the E-UTRAN (i.e., S8-4a˜S8-5a). The UE 10 performs a Service Request Procedure, thereby setting up a user plane as a path via the E-UTRAN (S8-6). The Service Request Procedure has been defined in clause 5.3.4.1 (UE triggered Service Request) of 3GPP TS 23.401 v9.3.0, and thus detailed explanations thereof will be omitted.
The S-GW 50 sends downlink data to the UE 10 through the E-UTRAN (via the eNodeB 21) (S8-7).
In FIG. 8, it is assumed that the UE 10 camps on the E-UTRAN cell. If the UE 10 of
FIG. 8 camps on the UTRAN/GERAN cell rather than the E-UTRAN cell, the UE 10 will respond to a paging which has passes through the UTRAN/GERAN (i.e., S8-4b S8-5b). And, if a user plane is set in S8-6, downlink data will be delivered to the UE 10 from the S-GW 50, via the UTRAN/GERAN (i.e., via the RNC/BSC 31 and the NodeB 32).
As aforementioned, since the network manages the UE's location as a unit of an ISR area, paging is performed as a unit of ISR area in order to transfer downlink data to the UE which is in an idle mode.
In an IMS network, an IMS voice service is provided to the UE over a Packet Switched (PS) domain or a Circuit Switched (CS) domain. Accordingly, the IMS network has to determine whether the UE can receive the IMS voice service over PS domain or CS domain.
In order for the SCC AS (Service Centralization and Continuity Application Server) in the IMS network to deliver a Mobile Terminating (MT) voice call to the UE, the SCC AS has to select an access domain (PS or CS domain) by executing Terminating Access Domain Selection (T-ADS) functionality. Here, the SCC AS has to select an access domain with consideration of the UE's current location, an access network's capability with respect to voice, etc.
When an ISR feature has been activated, the network will identify the UE's location at the ISR area. Therefore, the network can not check the UE's precise location due to the activated ISR (whether the UE is in the E-UTRAN or UTRAN/GERAN). In this case, if support of IMS voice over PS session is not consistent between the E-UTRAN and the UTRAN/GERAN that belong to the ISR area, this inconsistency may cause sequential paging from the CS domain to the PS domain, or from the PS domain to the CS domain for successful delivery of an MT voice call to the UE by the IMS network. For instance, in a state that the UE is camping on a cell where IMS voice over PS session is not supported, the IMS network may firstly select the PS domain for delivery of an MT voice call. In this case, call setup delay, a critical factor of a voice call service may increase, and a caller may terminate his or her call while waiting for call connection. This may cause call loss.
The above problems occur even in the case of the UE's intra-SGSN mobility shown in FIG. 2 and in the case of the UE's intra-MME mobility shown in FIG. 3. For instance, the UE moves from a first cell (e.g., RA1) served by the SGSN (network entity which provides a service to the UE with respect to the UTRAN/GERAN), and camps on a second cell (e.g., RA2) served by the same SGSN. In this case, since an activated ISR feature is kept, the UE does not have to perform location registration again on the network unless it leaves the routing area (RA2) registered through the SGSN, or the tracking area(s) registered through the MME. Here, the tracking area(s) registered through the MME support IMS voice over PS session. However, in an assumption that the second cell of the SGSN does not support IMS voice over PS session, if the IMS network delivers MT voice call to the UE over PS domain, the UE cannot receive the voice call. This may cause the aforementioned call termination and call loss.
In case of the intra-MME mobility shown in FIG. 3, the UE moves from a first cell of the E-UTRAN (e.g., TA1 of TAI list 1) served by the MME, and camps on a second cell served by the same MME (e.g., TA4 of TAI list 2). In this case, since an activated ISR feature is kept, the UE does not have to perform location registration again on the network unless it leaves the routing area registered through the SGSN, or the tracking area(s) (TAI list 2) registered through the MME. In the case of intra-MME mobility, call termination and call loss occurred in the case of intra-SGSN mobility may also occur.